note pvaldes <p>And you are not calling the function</p> <c> open(INFILE, '<','test.dat'); open(OUTFILE, '>','hex.dat'); while(<INFILE>){ chomp; #printf ("%#x", $line) > $line2; my $line2 = &capture_stdout($_) ; ### <--- see the & print OUTFILE $line2,"\n"; } sub capture_stdout(){ my $v; local *STDOUT; open(STDOUT, '>', \$v); printf ("%#x", $_); return $v; } close INFILE; close OUTFILE;</c> <p>In any case you can use pack for this, probably</p> 1013464 1013464